Dehydrogenation of isopropanol on a modified copper catalyst

The influence of plasmochemical treatments of the 5 wt % Cu/SiO₂ catalyst and cerium additives on the activity of the catalyst in isopropanol dehydrogenation was studied. After the catalyst was treated with high-frequency plasma in H₂ under the flow conditions, the conversion of alcohol increased. The reaction kinetics was studied under static conditions. The rate constant increased 1430-fold after the introduction of an optimum dose of Ce and treatment in Ar, O₂, and H₂ plasma and 550-fold after treatment with high-frequency plasma in H₂. The experimental activation energy increased in all instances; the activity grew because of the increase in the number of active centers. The promoting action of cerium was explained by the positive charge of the Ce^+α adatom, which initiated growth of the surface electron density; the influence of plasmochemical treatments was explained by the change in the number of structural defects and their character. Possible stepwise reaction schemes were considered based on ab initio quantum-chemical calculations.     

Convenient, rapid synthesis of rare earth orthochromites LnCrO by self-propagating high-temperature synthesis

Lanthanide orthochromites of general formula LnCrO₃ (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Lu) and YCrO₃ have been made by self-propagating high-temperature synthesis (SHS). Four different SHS reactions were found to form LnCrO₃: reaction of Ln₂O₃, Cr and CrO₃ with NaClO₄ or Ba (ClO₄)₂ in air; reaction of Ln₂O₃, Cr and CrO₃ in oxygen; reaction of LnCl₃, CrCl₃ and NaO₂ or Na₂O₂ in air and reaction of Ln (NO₃)₃, Cr and melamine in air. Reactions were studied by DTA and TGA experiments which showed exotherms and weight losses associated with the initiation temperatures (ca. 350°C) of the SHS reactions. Maximum reaction temperature T_c and propagation velocity U_c were measured for selected reactions. X-ray powder diffraction showed a single phase orthorhombic perovskite structure was produced in all reactions. Systematic changes in the lattice parameters, cell volume and pycnometrical densities were seen as a function of lanthanide atomic number. SHS prepared LnCrO₃ samples were all shown to be weak antiferromagnets. IR spectra for the LnCrO₃ materials showed bands at 635, 480, 440, 350 and 180 cm⁻¹.     

Photoluminescence studies on rare earth titanates prepared by self-propagating high temperature synthesis method

The laser-induced luminescence studies of the rare earth titanates (R2Ti2O7) (R=La, Nd and Gd) using 355 nm radiation from an Nd:YAG laser are presented. These samples with submicron or nanometer size are prepared by the self-propagating high temperature synthesis (SHS) method and there is no known fluorescence shown by these rare earths in the visible region. Hence, the luminescence transitions shown by the La2Ti2O7 near 610 nm and Gd2Ti2O7 near 767 nm are quite interesting. Though La3+ ions with no 4f electrons have no electronic energy levels that can induce excitation and luminescence processes in the visible region, the presence of the Ti3+ ions leads to luminescence in this region.     

Testing of nickel phosphate (NiP) catalyst for ethylbenzene oxydehydrogenation by means of isopropanol dehydration

It has been shown that NiP catalyst, if fresh, contains a high concentration of the same type acid-base surface centers as those participating in i-PrOH dehydration on -Al₂O₃. The concentration of these centers diminishes rapidly after a modification of NiP surface in a stream of ethylbenzene (EtPh) oxydehydrogenation products.

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, NiP - , , i-PrOH -Al₂O₃. NiP .

     

间歇式水热合成制备丝光沸石膜及其异丙醇脱水应用

采用市售廉价大孔α-Al₂O₃管作为基质材料,通过热浸渍法在管外表面涂敷晶种,随后在无模板剂体系下,利用新型的间歇式水热合成法制备丝光沸石膜。对比了传统加热和间歇式加热对丝光沸石膜形貌、结构及渗透蒸发异丙醇脱水分离性能的差异。考察了合成液中Na₂O/SiO₂、SiO₂/Al₂O₃和NaF/SiO₂物质的量之比在间歇式水热合成下对丝光沸石膜的影响。研究结果表明,当合成液中Na₂O/SiO₂、SiO₂/Al₂O₃和NaF/SiO₂物质的量之比分别为0.24、16.7和0.25时,制备的丝光沸石膜渗透蒸发异丙醇脱水分离性能最佳,在75℃下,对异丙醇/水(9:1,w/w)的渗透通量达5.60 kg·m^-2·h^-1,水对异丙醇的分离因数大于10 00...     

间歇式水热合成制备丝光沸石膜及其异丙醇脱水应用

采用市售廉价大孔α-Al₂O₃管作为基质材料,通过热浸渍法在管外表面涂敷晶种,随后在无模板剂体系下,利用新型的间歇式水热合成法制备丝光沸石膜。对比了传统加热和间歇式加热对丝光沸石膜形貌、结构及渗透蒸发异丙醇脱水分离性能的差异。考察了合成液中Na₂O/SiO₂、SiO₂/Al₂O₃和NaF/SiO₂物质的量之比在间歇式水热合成下对丝光沸石膜的影响。研究结果表明,当合成液中Na₂O/SiO₂、SiO₂/Al₂O₃和NaF/SiO₂物质的量之比分别为0.24、16.7和0.25时,制备的丝光沸石膜渗透蒸发异丙醇脱水分离性能最佳,在75℃下,对异丙醇/水(9∶1,w/w)的渗透通量达5.60 kg·m^-2·h^-1,水对异丙醇的分离因数大于10 000。     

钾和钴对微波法制备钼基催化剂的改性作用

在微波辐射下制备了Co_x-MoS₃-K_y/γ-Al₂O₃催化剂,考察了催化剂中K和Co的含量对其催化CO加氢合成低碳醇性能的影响。结果表明,添加适量的K和Co可以形成K-Mo-S相和Co-Mo-S相,改善催化剂性能的同时还可以避免活性组分的集聚及载体孔道的堵塞;K/Mo物质的量比为1.0,Co/Mo物质的量比为0.2时,有利于生成低碳混合醇,尤其是C₂₊醇。CO转化率为38.4%,总醇的收率为5.65%,C₂₊OH的选择性为80.5%。     

Solid state synthesis of tungsten carbide nanorods and nanoplatelets by a single-step pyrolysis

We report a simple and efficient single-step synthesis of tungsten carbide nanorods and nanoplatelets by direct pyrolysis of a hybrid composite material of 12-tungstophosphoric acid and hexadecyltrimethylammonium bromide in a closed Swagelok cell at 1000 degrees C. The product was characterized by XRD, TGA, SEM, TEM, XPS, and CV. The diameter of the nanorods is 30-50 nm, and the length varies from 200 to 500 nm. The size of the platelets is around 55 nm. The WC exhibits an interesting structural surface with kinks, steps, and terraces which is evidenced by HRTEM studies.     

Nanosized cobalt-based catalyst prepared by supercritical phase condition for Fischer-Tropsch synthesis

A series of nanosized Co/Zn/Mn/K composite catalysts for Fischer-Tropsch synthesis (FTS) were prepared by supercritical fluid drying (SCFD) method and common drying (CD) method. The nanosized cobalt-based catalysts were characterized by XRD, TEM and BET techniques. Their catalytic performances were tested in a slurry-bed reactor under FTS reaction conditions. The drying and crystallization were carried out simultaneously during SCFD, therefore, the catalysts prepared by SCFD method have ideal structure and show the FTS performance superior to the others prepared by CD method. The FTS activity and selectivity were improved via adding Zn, Mn and K promoters, and less CH₄ and CO₂ as well as higher yield of C₅₊ products were achieved. The optimal performance of a 92% CO conversion and a 65% C₅₊ product yield was obtained over a catalyst with the component of Co/Zn/Mn/K = 100/50/10/7. Furthermore, the catalytic performance was studied under the conditions of liquid-phase and supercritical phase slurry-bed, and C₅₊ product yield were 57.4% and 65.4%, respectively. In summary, better catalytic performance was obtained using the nanosized catalyst prepared by SCFD method under supercritical reaction conditions, resulting in higher conversion of CO, less CO₂ byproduct, and higher yield of C₅₊ products.     

Copper-magnesium oxide catalyst based on modified dolomite

Novel highly active copper-magnesium oxide catalysts based on modified dolomite were synthesized. They are of superior performance in comparison with catalyst materials (MTM, Birm, Pyrolox, MZHF) which are widely used currently in purification of water from iron. The influence of the nature of the copper precursor and concentration of impregnation solutions on the activity and phase composition of catalysts was found.     

添加表面活性剂两步沉淀法制备甲醇催化剂

采用添加表面活性剂两步沉淀法制备了具有高表面铜相对浓度的超细甲醇合成催化剂。以组成为H2/CO/CO2/N2=66/27/3/4(体积比）的原料气对催化剂进行了活性评价。结果表明,该催化剂比传统并流沉淀法制备的铜基催化剂活性提高47.9%,比两步沉淀法和添加表面活性剂并流沉淀法制备的铜基催化剂活性分别提高9.3%和16.8%。利用SEM、XRD及XPS方法对催化剂的结构、形貌和表面金属组成进行了表征。     

Highly active catalyst for vinyl acetate synthesis by modified activated carbon

A new zinc acetate catalyst which was prepared from modified activated carbon exhibited extreme activity towards the synthesis of vinyl acetate.The activated carbon was modified by nitric acid,vitriol and peroxyacetic acid(PAA).The effect on specific area, structure,pH and surface acidity groups of carriers by modification was discussed.Amount of carbonyl and carboxyl groups in activated carbon was increased by peroxyacetic acid treatment.The productivity of the new catalyst was 14.58%higher than that of...     

A zirconium modified Co/SiO2 Fischer-Tropsch catalyst prepared by dielectric-barrier discharge plasma

Co/SiO₂ and zirconium promoted Co/Zr/SiO₂ catalysts were prepared using dielectric-barrier discharge (DBD) plasma instead of the conventional thermal calcination method. Fischer-Tropsch Synthesis (FTS) performances of the catalyst were evaluated in a fixed bed reactor. The results indicated that the catalyst treated by DBD plasma shows the higher FTS activity and yield of heavy hydrocarbons as compared with that treated by the conventional thermal calcination method. Increase in CO conversion was unnoticeable on the Co/SiO₂ catalyst, but significant on the Co/Zr/SiO₂ catalyst, both prepared by DBD plasma. On the other hand, heavy hydrocarbon selectivity and chain growth probability (α value) were enhanced on all the catalysts prepared by the DBD plasma. In order to study the effect of the DBD plasma treatment on the FTS performance, the catalysts were characterized by N₂-physisorption, H₂-temperature programed reduction (H₂-TPR), H₂-temperature-programmed desorption (H₂-TPD) and oxygen titration, transmission electron microscope (TEM) and X-ray diffraction (XRD). It was proved that, compared with the traditional calcination method, DBD plasma not only could shorten the precursor decomposition time, but also could achieve better cobalt dispersion, smaller Co₃O₄ cluster size and more uniform cobalt distribution. However, cobalt reducibility was hindered to some extent in the Co/SiO₂ catalyst prepared by DBD plasma, while the zirconium additive prevented significantly the decrease in cobalt reducibility and increased cobalt dispersion as well as the FTS performance.     

Branched polyethylene prepared by in situ copolymerization of ethylene with monotitanocene and modified methylaluminoxane catalyst

Branched polyethylene was synthesized in heptane used as a polymerization medium with monotitanocene catalyst composed of η⁵‐pentamethylcyclopentadienyl tribenzyloxy titanium and modified methylaluminoxane (mMAO) that contained different amounts of residual trimethylaluminum (TMA). The residual TMA more strongly reduced Ti(IV) complexes to Ti(III) and Ti(II) ones, and Ti(IV) active species were suggested to be more effective for ethylene polymerization. Influences of the polymerization temperature and Al/Ti molar ratio on the catalytic activity and the degree of branching, branch length, and molecular weight of polyethylene were investigated. The obtained polymers were confirmed by ¹³C NMR to be higher molecular weight polyethylene containing significant amounts of isolated ethyl branches, butyl branches, or both. Branched polyethylene was prepared by the in situ copolymerization of ethylene with 1‐butene and 1‐hexene, which were formed through a proposed mechanism including metallcycloheptane and metallcyclopentane intermediates of Ti(II) species that were produced by the reaction of Ti(IV) complexes with TMA coexisting in mMAO. There was a remarkable increase in the chance of 1‐butene being produced from metallcyclopentane of Ti(II) intermediates with an increase in the polymerization temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4258–4263, 2000     

New lanthanide silicates based on anionic silicate chain, layer, and framework prepared under high-temperature and high-pressure conditions

Three new lanthanide silicates K(1.25)Gd(1.25)Si(2.5)O(7.5) (denoted as GdSiO-CJ7), Cs(3)TbSi(8)O(19)·2H(2)O (denoted as TbSiO-CJ8), and Cs(3)DySi(6)O(15) (denoted as DySiO-CJ9) were synthesized by using a high-temperature and high-pressure hydrothermal method. Their structures determined by single-crystal X-ray diffraction revealed anionic silicate chain, layer and framework, which are further connected with LnO(n) polyhedra to form novel lanthanide silicate frameworks. The structure of GdSiO-CJ7 consists of unbranched silicate chains [Si(5)O(15)](10-) extending along the b axis, which are linked together by edge-sharing linked GdO(6) and GdO(8) chains along the c axis to form a 3-D framework with two types of 10-ring channels along the [010] and [001] directions, respectively. The structure of TbSiO-CJ8 consists of double 4,8-net sheets [Si(8)O(19)](6-) built up from SiO(4) tetrahedra, which are linked together via TbO(6) octahedra to form a 3-D framework with 8-ring channels along the [100] and [010] directions. The structure of DySiO-CJ9 is based on a 3-D silicate framework [Si(6)O(15)](6-) with 6-rings, where DyO(6) octahedra are located between two adjacent 6-rings and connected with six Si atoms via O atoms. The photoluminescence photoluminescence properties of TbSiO-CJ8 and EuSiO-CJ8 were investigated.     

CS2对完全液相法制备的 Cu-Zn-Al催化剂上合成气制DME反应性能的影响

实验以CS₂为硫源,考察硫对完全液相法制备Cu-Zn-Al催化剂活性的影响,并用X射线粉末衍射(XRD)、氢气程序升温吸附(H₂-TPR)、氨气程序升温脱附(NH₃-TPD)等方法对催化剂性能进行了表征。结果表明,对完全液相法制备的Cu-Zn-Al催化剂而言,加入小于4mg/L 的CS₂对催化剂的活性影响不大;催化剂的活性随着加入硫含量的增加,下降程度增大。     

A zirconium modified Co/SiO2 Fischer-Tropsch catalyst prepared by dielectric-barrier discharge plasma

Co/SiO₂ and zirconium promoted Co/Zr/SiO₂ catalysts were prepared using dielectric-barrier discharge（DBD） plasma instead of the conventional thermal calcination method.Fischer-Tropsch Synthesis（FTS） performances of the catalyst were evaluated in a fixed bed reactor.The results indicated that the catalyst treated by DBD plasma shows the higher FTS activity and yield of heavy hydrocarbons as compared with that treated by the conventional thermal calcination method.Increase in CO conversion was unnoticeable on the Co/SiO₂ catalyst,but significant on the Co/Zr/SiO₂ catalyst,both prepared by DBD plasma.On the other hand,heavy hydrocarbon selectivity and chain growth probability （a value） were enhanced on all the catalysts prepared by the DBD plasma.In order to study the effect of the DBD plasma treatment on the FTS performance,the catalysts were characterized by N₂-physisorption,H2-temperature programed reduction（H₂-TPR）,H₂-temperature-programmed desorption（H₂-TPD） and oxygen titration,transmission electron microscope（TEM） and X-ray diffraction（XRD）.It was proved that,compared with the traditional calcination method,DBD plasma not only could shorten the precursor decomposition time,but also could achieve better cobalt dispersion,smaller Co₃O₄ cluster size and more uniform cobalt distribution.However,cobalt reducibility was hindered to some extent in the Co/SiO₂ catalyst prepared by DBD plasma,while the zirconium additive prevented significantly the decrease in cobalt reducibility and increased cobalt dispersion as well as the FTS performance.     

Three-dimensional mesoporous titanosilicates prepared by modified sol-gel method: Ideal gold catalyst supports for enhanced propene epoxidation

Mesoporous titanosilicates with 1-12 mol % Ti content and with three-dimensional wormhole-like mesoporosity are prepared by a modified sol-gel technique. Sorption analysis shows that there is little change in the surface properties with increasing Ti concentration in the samples, implying that Ti atoms either are well-dispersed on the walls of the silica matrix or are present inside the framework with no pore blocking effect. Spectroscopic analysis shows that the Ti atoms are atomically dispersed in the silica matrix even at very high Ti concentration and there is no observable Ti aggregate (anatase) present in the samples. These titanosilicate samples after Au deposition followed by trimethylsilylation (for enhanced hydrophobicity) are highly efficient catalysts for vapor-phase propene epoxidation using O2 and H2. It was possible to achieve commercially desirable performance with about 7% propene conversion, >90% propene oxide selectivity, and about 40% hydrogen efficiency.